Heterodyne measurements of electron cyclotron emission from Alcator A and absolute submillimeter receiver calibration

Electron cyclotron emission (ECE) from thermal plasmas in the Alcator A tokamak for harmonics from 2nd through 5th and up to the 7th harmonic for nonthermal plasmas have been observed in the frequency range of 400–800 GHz using a sensitive, low-noise submillimeter heterodyne receiver. The sensitivity of the receiver (∼10−20 W Hz−1) allowed for the measurement of 4th and 5th harmonic ECE from thermal plasmas with Te≊800 eV. The receiver was absolutely calibrated and its field of view was experimentally determined. A careful analysis has been made to relate the receiver calibration to the plasma-emitting volume, taking into account radiation coherence time, wall reflections, polarization scrambling, window losses, and aperture restrictions.